Conventionally, screen capture (also referred to as, for example, “screen shot” or “screen dump”) is known of storing content to be displayed on a screen by display processing of electronic data such as electronic document or images as still image data. This screen capture function is provided by, for example, an operating system, or can be realized by executing screen capture software. Hence, there is a problem that content such as personal information or copyrighted work which is undesirable to be replicated is easily replicated.
Therefore, for example, a method is proposed of restricting browsing of content without browsers to which a function of disabling screen capture is added. However, if a user takes a picture of a screen, it is still possible to replicate display content on the screen.
With regard to this problem, Patent Literature 1 discloses a technique of preventing digital shoplifting of capturing an image of content of a book using a digital camera. More specifically, digital watermark is printed on pages of a book. Further, when the digital camera detects digital watermark from captured images, processing is performed of forbidding storage or transmission of images, or tessellating the captured images or destroying readability of letters.